1. Field of the Invention
The present invention relates to ladder polymers, and particularly to an organic semiconductor polymer that is a carbazole-based ladder polymer.
2. Description of the Related Art
By definition, ladder polymers have a distinctive architecture, whereby the chain consists of an uninterrupted sequence of rings, fused together in such a way that adjacent rings share two or more atoms in common, resulting in a constrained chain conformation. Possessing a backbone of fused aromatic rings, a fully conjugated ladder polymer is intrinsically free of possible torsional disorders that result from s-bond rotations in between the monomeric units. Without the interruption from these conformational disorders, as a result, the coherent p-conjugation length of a coplanar ladder backbone is much more extended. Such a well-defined conformation would afford a faster intra-chain charge/phonon transport, and a longer exciton diffusion length compared to conjugated polymers with free rotating torsional motions. This argument is further corroborated by the unparalleled electronic and thermal conductivity of graphene nanoribbons, which can be viewed as insoluble ladder polymers composed of only sp2 carbon atoms. Combining the advantages of conventional polymeric materials such as solution processability and structural versatility, ladder polymers emerge as promising candidates for next-generation synthetic organic materials with breakthrough performances.
The synthesis of a well-defined ladder polymer, however, is a challenging task because of (i) the potential structural defects originated from moderately efficient ring-closing reactions, and (ii) the often poor solubility of structurally rigid intermediates or products. In an effort to overcome these obstacles, a highly efficient synthetic method and a rationally designed structural characteristic that enables solubility need to be achieved and integrated simultaneously.
Thus, an organic semiconductor polymer solving the aforementioned problems is desired.